This is a good, informative post. I have met teachers from countries such as Nigeria and the Philippines where English is a required language to be learned by everyone. I find it a bit unfair that teachers from these countries are classified as "non-native" speakers. The Philippines have a heavy American influence and their accent even sounds like it, hence the large number of call centers set up by USA companies there to handle customer service issues from back home. The Nigerian accent while distinct is much easier to comprehend than the Indian accent as well as Native English accents from Australia and South Africa IMO, and the Nigerian guy told me he started learning the language from birth. Hopefully as the world become smaller these teachers become more accepted.

As for a non-native speaker contributing much more than native speaking teachers, look no further than the Turnoi poster. He has given much more than the rest of the regular posters on this board.